Fog stabilizers for photographic emulsions

ABSTRACT

A PHOTOGRAPHIC SILVER HALIDE EMULSION OR PHOTOGRAPHIC ELEMENT CONTAINING A FOG-STABILIZING AMOUNT OF A THIONAMIDE, E.G., A 3 SUBSTITUTED THIAZOLINE-2-THIONE, N,N-DISUBSTITUTED DITHIOCARBAMIC ESTER OF AN N,N,N&#39;&#39;,N&#39;&#39;-TETRASUBSTITUTED THIOUREA, WHICH CONTAINS AT LEAST ONE ACID GROUP IN THE MOLECULE IS DISCLOSED. THE ACID GROUP OR GROUPS CONTAINED IN THE THIONAMIDE MOLECULE SHOULD BE ONES WHICH WILL CONFER A NEGATIVE CHARGE TO THE THIONE AT A PH OR 5 OR BELOW AND IS EXEMPLIFIED BY CARBOXYLIC OR SULFONIC ACID GROUPS. SILVER HALIDE COMPLEXES OF THIONAMIDES AND DEVELOPING PHOTOGRAPHIC ELEMENTS ARE ALSO DESCRIBED.

Un ited states Patent Olhce 3,598,598 Patented Aug. 10, 1971 3,598,598FOG STABILIZERS FOR PHOTOGRAPHIC EMULSIONS Arthur H. Herz, Rochester,N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing.Filed Oct. 1, 1968, Ser. No. 764,332

Int. Cl. G03c N34 US. Cl. 96-109 20 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF THE INVENTION Field of the invention This inventionrelates to new and improved antifoggants and stabilizers forphotographic elements and to photographic silver halide emulsionscontaining said antifoggants and stabilizers therein. The invention alsorelates to silver halide complexes and to a process of developingphotographic elements in the presence of new and improved antifoggants.

Description of the prior art During development of a silver halideemulsion, small amounts of silver halide are reduced to metallic silverregardless of whether or not they have been exposed. This reduction ofsilver ion produces a background fog which is more specifically referredto as chemical fog.

Chemical fog, apparent in most silver halide systems, has been reducedby prior art methods of processing exposed silver halide material in thepresence of compounds which restrict development of unexposed silverhalide. Such compounds can be incorporated in the silver halide emulsionor in the processing solutions for developing such silver halideemulsions. Compounds which have been found to have a chemical foginhibiting effect on emulsions which have been subjected to hightemperature and high humidity conditions are referred to as emulsionstabilizers. On the other hand, compounds which have been found to havechemical fog inhibiting effects on emulsions which have not been exposedto adverse storage conditions are referred to as antifoggants. Althougha large number of emulsion stabilizers and anti foggants have been usedin the prior art, many of these compounds cause undesirable losses inemulsion speed and contrast and others lack adequate compatibility withemulsion gelatin.

Thionamides have been used in the past as antifoggants in silver halideemulsions. Such compounds generally contain at least one hydrogen atomon the amidic nitrogen and exist in tautomeric equilibria between thethione and sulfhydryl structure. However, these compounds have apropensity to desensitize fast silver halide emulsions and, therefore,are generally used in concentrations of less than 50 milligrams per moleof silver to prevent objectionable loss of emulsion sensitivity.

SUMMARY OF THE INVENTION According to one embodiment of this invention,there is incorporated into the silver halide emulsion of aphotographicelement or in a layer contiguous to the silver halide emulsion, a fogstabilizing amount of an acrylic or monocyclic thionamide, saidthionamide containing at least one acid group which will confer anegative charge to the thionamide at a pH of 5 or below. These compoundsstabilize the emulsion against fog when the dried emulsion has beensubjected to a prolonged high humidity and temperature incubation periodwithout adversely effecting other sensitometric properties.

According to another embodiment of the invention, a photographic elementcomprising a support coated with at least one silver halide emulsionlayer is developed in the presence of one of the previously describedthionamides. Preferably, the thionamide is present in the photographicelement but it can be present elsewhere in the systeme.g., in thedeveloper.

According to still another embodiment of this invention, there areprovided wateror alkali-soluble silver complexes of the previouslydescribed thionamides.

DESCRIPTION OF THE PREFERRED EMBODIMENT Thionamides which are suitablyused in the practice of this invention include those having the generalformula wherein X represents sulfur, oxygen or an iso-electronic group,'e.g., -CH=CH (where R and R are taken together) or =N'R where R is analiphatic group or a substituted aliphatic group, R R and R when takenseparately, are aliphatic groups or substituted aliphatic groups, R andR when taken together, represent an alkylene group, and R and R whentaken together with the nitrogen atom to which they are attached,represent a heterocyclic group, at least one of the groups containing anacid substituent.

One group of thionamides which can be used in the practice of thisinvention are 3-substituted thiazoline-2 thiones which have thestructure wherein R is an aliphatic group, e.g., an alkyl chaincontaining up to 10 carbon atoms which can be substituted with one ormore groups such as carboxyl, sulfonyl, etc.; R and R can each behydrogen, an aliphatic or substituted aliphatic radical, e.g., a ketogroup, a carboxyl group or an alkyl group containing up to 10 carbonatoms, which alkyl group can be further substituted with one or moreother groups such as carboxyl, sulfonyl, hydroxy, an ester group, etc.;and at least one of R R and R contains an acid substituent such as acarboxylic or sulfonic acid group. Compounds having the above structurewhich can be used in the practice of this invention are set forth belowwherein the groups R, R and R are as specified:

CH3 (H) -CHCOzH -CH; --C CH3 -CHuCHzSOaH- -CH3 -11 -CHCO2H CH3 CHCHzCOzH -CH3 -CH3 CO2H -CH -CH2COzH -H Another group of thionamideswhich can be used in the practice of this invention areN,N-disubstituted dithiocarbamic esters having the structure \N|J-S R1R2 5 wherein R R and R are the same as defined above. Thus, the groupand R can be a substituted aliphatic group having from 3 to carbon atomsand containing a carboxylic or sulfonic acid group such as Examples ofsuch compounds include the following wherein the variable groups are asindicated:

Same as above.

A further group of thionamides which can be used areN,N,N,N'-tetrasubstituted thioureas having the structure groupscontaining an acid substituent such as a carboxylic or sulfonic acidgroup.

Other groups of thionamides which can be used include those having thegeneral formulas wherein R, R R and R are the same as previouslydefined.

The thionamide can be incorporated into the silver halide emulsion of aphotographic element or in a layer contiguous to the silver halideemulsion in any amount which Will stabilize the silver halide emulsionagainst fog. In general, a concentration of the thionamide in an amountof from about 0.05 to about 30, preferably about 0.6 to about 10.0 gramsper mole of silver in the silver halide emulsion can be used with goodresults.

The preparation of photographic silver halide emulsions such as aresuitably stabilized with the thionamide typically involves threeseparate operations: (1) emulsification and digestion of silver halide,(2) the freeing of the emulsion of excess water-soluble salts, suitablyby washing with water, and (3) the second digestion or after-ripening toobtain increase demulsion speed or sensitivity. (Mees, The Theory of thePhotographic Process, 1954.) The thionamide can 'be added to theemulsion before the final digestion or after-ripening or it can be addedimmediately prior to the coating.

The silver halide emulsion of a photographic element containing theantifoggants of this invention can contain conventional addenda such asgelatin plasticizers, coating aids, and hardeners such as aldehydehardeners, e.g., formaldehyde, mucochloric acid, glutaraldehydebis(sodium bisulfite), maleic dialdehyde, aziridines, dioxanederivatives and oxypolysaccharides. Spectral sensitizers which can beused are the cyanines, merocyanines, complex (trinuclear) cyanines,complex (trinuclear) merocyanines, styryls, and hemicyanines.Sensitizing dyes useful in sensitizing such emulsions are described, forexample, in US. Pats. 2,526,632 of Brooker and White issued Oct. 24,1950, and 2,503,776 of Sprague issued Apr. 11, 1950. Developing agentscan also be incorporated into the silver halide emulsion if desired orcan be contained in a contiguous layer. Various silver salts can be usedas the sensitive salt such as silver bromide, silver iodide, silverchloride, or mixed silver halides such as silver chlorobromide, silverbromoiodide and the like. The silver halides used can be those whichform latent images predominantly on the surface of the silver halidegrains or those which form latent images inside the silver halidecrystals such as described in US. Pat. 2,592,250 of Davey and Knottissued Apr. 8, 1952.

The silver halide emulsion layer of a photographic element containingthe antifoggants of the invention can contain any of the hydrophilic,water-permeable binding materials suitable for this purpose. Suitablematerials include gelatin, colloidal albumin, polyvinyl compounds,cellulose derivatives, acrylamide polymers, etc. Mixtures of thesebinding agents can also be used. The binding agents for the emulsionlayer of the photographic element can also contain dispersed polymerizedvinyl compounds. Such compounds are disclosed, for example, in US. Pats.3,142,568 of Nottorf issued July 28, 1964; 3,193,386 of White issuedJuly 6, 1965; 3,062,674 of Houck, Smith and Yudelson issued Nov. 6,1962; and 3,220,844 of Houck, Smith and Yudelson issued Nov. 30, 1965;and include the water insoluble polymers of alkyl acrylates andmethacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates andthe like.

The silver halide emulsion of a photographic element containing theantifoggants of the invention can be coated on a wide variety ofsupports. Typical supports are cellulose nitrate film, cellulose esterfilm, polyvinyl acetal film, polystyrene film, poly(ethyleneterephthalate) film and related films or resinous materials as well asglass, paper, metal and the like. Supports such as paper which arecoated with a-olefin polymers, particularly polymers of a-olefinscontaining two or more carbon atoms, as exemplified by polyethylene,polypropylene, ethylenebutene copolymers and the like can also beemployed.

The sensitometric characteristics of the photographic emulsionscontaining the antifoggants of the invention can be further enchanced byincluding in the emulsions a variety of hydrophilic colloids such ascarboxymethyl protein of the type described in U.S. Pat. 3,011,890 ofGates, Jr., Miller and Koller issued Dec. 5, 1961, and polysaccharidesof the type described in Canadian Pat. 635,206 of Koller and Russellissued Jan. 23, 1962.

Photographic emulsions containing the antifoggants of the invention canalso contain speed-increasing compounds such as quaternary ammoniumcompounds, polyethylene glycols or thioethers. Frequently, usefuleffects can be obtained by adding the aforementioned speed-increasingcompounds to the photographic developer solutions instead of, or inaddition to, the photographic emulsions.

Photographic elements containing the antifo ggants of the instantinvention can be used in various kinds of photographic systems. Inaddition to being useful in X-ray and other non-optically sensitizedsystems, they can also be used in orthochromatic, panchromatic andinfrared sensitive systems. The sensitizing addenda can be added tophotographic systems before or after any sensitizing dyes which areused.

Silver halide emulsions containing the antifoggants of the invention canbe used in color photography, for example, emulsions containingcolor-forming couplers or emulsions to be developed by solutionscontaining couplers or other color-generating materials, emulsions ofthe mixed-packet type such as described in U.S. Patent 2,698,- 794 ofGodowsky issued J an. 4, 1955; in silver dye-bleach systems; andemulsions of the mixed-grain type such as described in U.S. Pat.2,592,243 of Carroll and Hanson issued Apr. 8, 1952.

Silver halide emulsions containing the antifoggants of the invention canbe sensitized using any of the wellknown techniques in emulsion making,for example, by digesting with naturally active gelatin or varioussulfur, selenium, tellurium compounds and/or gold compounds. Theemulsions can also be sensitized with salts of noble metals of GroupVIII of the Periodic Table which have an atomic weight greater than 100.

Silver halide emulsions containing the antifoggants of the invention canbe used in diffusion transfer processes which utilize the undevelopedsilver halide in non-image areas of the negative to form a positive bydissolving the undeveloped silver halide and precipitating it on areceiving layer in close proximity to the original silver halideemulsion layer. Such processes are described in U.S. Patents 2,352,014of Rott issued June 20, 1944; 2,543,181 of Land issued Feb. 27, 1951;and 3,020,155 of Yackel, Yutzy, Foster and Rasch issued Feb. 6, 1962.The emulsions can also be used in diffusion transfer color processeswhich utilize a diffusion transfer of an imagewise distribution ofdeveloper, coupler or dye, from a lightsensitive layer to a secondlayer, while the two layers are in close proximity to one another.Silver halide emulsions containing the antifoggants of the invention canbe processed in stabilization processes such as the ones described inU.S. Pat. 2,614,927 of Broughton and Woodward issued Oct. 21, 1952, andas described in the article Stabilization Processing of Films and Papersby H. D. Russell, E. C.

Yackel and J. S. Bruce in P.S.A. Journal, Photographic Science andTechnique, volume 16B, October 1950.

While it is preferred to utilize the antifoggants of the invention byincorporating them directly into a photographic element, theantifoggants could also be utilized by incorporating them into aphotographic developer to control development fog.

The antifogging agents of this invention can be incorporated toadvantage during manufacture in silver halide emulsions representing thevariations described above. Moreover, fog control in binderless silverhalide films prepared by vapor deposition of silver halide on a suitablesupport can be achieved by coating the antifogging agents of theinvention over the vapor deposited layer of silver halide.

Combinations of all the above-mentioned addenda can be used if desired.

While the antifoggant action of the thionamide compounds of thisinvention are particularly advantageous, their ability to complex withmetal ions, especially with silver ions, warrants their use in numerousphotographic systems. Thus, they can be utilized in silver halidediffusion transfer systems; as silver halide grain growth agents topromote Ostwald ripening; as fixing agents; and as stabilization agentsfor unexposed silver halide in stabilization processing systems asdescribed, for example, in Broughton et al. U.S. Patent 2,614,927 issuedOctober 21, 1952. The thiones of this invention can also be used to formintramolecular salts or chelates with silver ions which, when coated ina suitable binder on a suitable support form light-sensitive layers asdescribed in copending application Ser. No. 764,298 of Haist et al.entitled Photosensitive Compositions Comprising Silver Complexes of3-Substituted-4-Thiazoline-2-Thiones and Photosensitive ElementsComprising Such Compositions filed concurrently herewith. The stabilityof these silver complexes will withstand extreme keeping conditionspermitting their incorporation into photographic elements as a silversource for physical development and used, for example, in systems of thetype described in Agfa British Pat. 920,- 277 issued Mar. 6, 1963; KodakBelgian Pat. 672,283 issued Mar. 1, 1966; and copending application Ser.No. 764,330 of Bass entitled Photographic Element, Composition andProcess filed concurrently herewith. The dual properties of stabilityand light sensitivity of these silverthione complexes allow them to beutilized with lightsenstive catalysts, which can or cannot bephotoconductors, in a bifunctional photographic element containing twolight-sensitive components which can be treated selectively to producetwo independent images. Alternatively, these silver complexes can beutilized in image reproduction systems in combination with a reducingagent and a light-sensitive catalyst as described in Shepard et al. U.S.Pat. 3,152,903 issued Oct. 13, 1964.

The invention can be further illustrated by the following examples orpreferred embodiments thereof, although it will be understood that theseexamples are included merely for purposes of illustration and are notintended to limit the scope of the invention.

In the following examples, the stabilizer compound is neutralized by theaddition of a base before addition to the emulsion where it is necessaryto maintain the pH of the emulsion constant.

EXAMPLE 1 Photographic emulsions .are prepared by adding thionamideshaving the formula wherein R is defined in Table 1, to separate portionsof a high speed gold and sulfur sensitized bromoiodide emul- 8 sion.Each emulsion sample is coated on a cellulose ace- 50 at 68 F. for fiveminutes. The photographic results tate film support at a coverage of 350milligrams of silver are set forth in Table 2.

TABLE 2 2 week incubation at 120 F. and 50% Stabilizer compound Freshrelative humidity Relative Relative R4 gJmole Ag speed Fog speed FogControl 100 0.10 0.66 -CH2COZH 3.0 102 0.09 107 0.12 -OH2CHzCOzH.. 3.0105 0.10 118 0.15 CH CHgOH2COzH 3.0 105 0.17 110 0.28

and 840 milligrams of gelatin per square foot. A sample EXAMPLE 3 f eachfilm coating 18 exposed an lmenfilty S.cale Photographic emulsions areprepared by adding stabisitometer, processed for four minutes at 68 F.1n Kodak lizer compounds having the formula Developer D-19, fixed,washed and dried. The photographic results obtained from these tests arelisted in Table 1. 20 S TABLE 1 2 week lneu- N bation at Fresh sigl andR4 re a We Relative Fog hiimidity, wherein R and R are defined in Table3 to separate por- Thlonamldel R4 Ag speed {0g tions of a high speedgold and sulfur sensitized bromo- Control 100 0 00 0. iodide emulsioncontaining a spectral sensitizer. Each :8g: 6 3; g; g g emulsion sampleis coated on a cellulose acetate film support at a coverage of 350milligrams of silver and 840 u 30 milligrams of gelatin per square foot.A sample of each It W111 be seen that the emu1s10n contammg a thionfilmcoating is exposed on an intensity scale sensitomamide having a carboxylsubstituent is much more effeceter, processed for five minutes at 68 F.in Kodak Detive in preventing the growth of incubauon fog than is aveloper DK50, fixed, washed and dried. The photographic thionamide whichdoes not contain an and substituent. results obtained from these testsare listed in Table 3.

TABLE 3 Incubation at F. and relative humidity Stabilizer compound Fresh1 week g./mole Relative Relative 2 Weeks, R4 R5 Ag speed Fog speed Fogfog Control 100 0.12 83 0. 34 1.12

-C]}HCO2H -CO2H 3.0 97 0.10 0.13 0.13

-CH2CH2C 02H CHzS O2(CH2)3CH3 0. 3 102 O. 11 97 0.17 O. 35

EXAMPLE 2 EXAMPLE 4 1 Process of Example 1 is repeatefi except that the5 The process of Example 3 is repeated substituting for stabllizercompounds added to the emulsions have the forthe Stabilizer compoundstherein a thionamide having the mula formula 8 s r mo CHzOzC-l HsC-KlTI/HaC- wherein R is defined in Table 2. The emulsions also contain aspectral sensitizer and, in several samples, an 60 In several samples,an additional compound as indicated additional compound or compounds asindicated in Table in Table 4 is included. The photographic resultsobtained 2. Development is accomplished in Kodak Developer DK- 7 arehsted in Table 4.

TABLE 4 1 week incubation at 120 F. and 45% relative Fresh humidityConcentration of Additional compound stabilizer compound in andconcentration Relative Relative ./mole Ag in gJmole Ag speed Fog speedFog Control 100 0. 12 82 0. 34 3. 0 120 0. 14 0. 17 ControlPoly(thi0diethylene 182 0. 24 1. 2

glutarate) (1.0). 3. 0 do 214 0. 21 178 0. 34 191 0. 21 1. 2 186 0. 19151 0. 33

9 EXAMPLE The process of Example 3 is repeated using as the is alsotested for its ability to stabilize an emulsion. The photographicresults are set forth in Table 6.

TAB LE 6 Dithioearbamate Incubation at 120 F. and R3 50% relativehumidity Fresh 1 week 2 Relative Relative Weeks, R R gJinole Ag SpeedFog Speed Fog Fog Control 100 0. 17 62 0. 41

m 0. 27 100 0.13 76 0. 0 N CH -C 02H Containing no acid 0.27 29. 5 0.22 1. 0

group. Control 100 0.13 57 0. 48 1. 21

(C O CH2)2N-.-- 3.0 100 0. 09 91 0. 09 0. 09

CH2- C 0 2H Control 100 0. 16 0. 81

N on ong)zs 03 m CH stabilizer a thionamide having the formula EXAMPLE 7I s H3O\ For the purpose of comparison, there is also tested an emulsioncontaining a non-acid group containing thionamide having the formula CHS The photographic results are set forth below in Table 7.

TABLE 7 s 40 Two weeks I an 0 H3 CHZC 02 CH? C Fresh relative humidit yThiourea in Relative Relative 311 013 0 CH3 EJ g speed Fog speed Fog Thephotographic results obtained are set forth in Table 5. control- 1000.14 54 0. 35 0.9- 8O 0. 11 65 0. 14

TABLE 5 Incubation at 120 F. and

% relative humidity Fresh 1 week 2 Relative Relative weeks, ThionamideG./mole Ag spee Fog speed Fog Fog Control 100 0. 12 59 0. 48 1. 16Containing acid group 0.3 95 0. 11 94 0.14 0. 25 Containing no acidgroup.-- 0.3 78 0. 11 1. 0 1. 2

EXAMPLE 6 This example illustrates the use of dithiocarbamatescontaining acid groups as stabilizers for photographic emulsions. Theprocess of Example 2 is repeated using as the stabilizer compounddithiocarbamates having the are as defined in Table 6. For purpose ofcomparison, a non-acid group containing dithiocarbamate having the HazeIn the foregoing Table 4, the pyridinium salt used is 7,18-diazo-6,19dioxotetracosane 1,24-bis(pyridinium perchlorate) The results in theabove tables show that the compounds of this invention prevent thegrowth of incubation fog when incorporated in photographic emulsions.

Although the invention has been described in considerable detail withreference to certain embodiments thereof, it will be understood thatvariations and modifications can be effected without departing from thespirit and scope of the invention as described hereinabove and asdefined in the appended claims.

I claim:

1. A composition comprising a silver halide emulsion containing afog-stabilizing amount of an acylic or monocyclic thionamide, saidthionamide containing at least one carboxylic or sulfonic acid groupwhich will confer a negative charge to the thionamide at a pH of 5 orbelow.

11 2. The composition of claim 1 wherein said thionamide is present inan amount of about 005 gram to about 30.0 grams per mole of silver insaid silver halide emulsion.

3. The composition of claim 1 wherein said thionamide has the structurewherein X is sulfur, oxygen or an iso'electronic group, R R and R whentaken separately, are aliphatic groups having up to 10 carbon atoms orsubstituted aliphatic groups, R and R when taken together, represent analkylene group and R and R when taken together with the nitrogen atom towhich they are attached, represent a heterocyclic group.

4. The composition of claim 1 wherein said thionamide has the structure/C=S R wherein R is an aliphatic group or a substituted aliphatic groupcontaining up to carbon atoms and R and R are hydrogen, aliphatic groupsor substituted aliphatic groups containing up to 10 carbon atoms, atleast one of said groups containing a carboxylic or sulfonic acidsubstituent.

5. The composition of claim 3 wherein X in said thionamide is sulfur andat least one of said groups R R and R contains a carboxylic or sulfonicacid substituent.

6. The composition of claim 3 wherein X in said thionamide representsthe group --NR, R being an. aliphatic or substituted aliphatic grouphaving from 1-10 carbon atoms, and at least one of said groups R, R Rand R contains a carboxylic or sulfonic acid substituent.

7. A photographic element comprising a support coated with a silverhalide layer, said element containing a fog-stabilizing amount of anacylic or monocyclic thionamide, said thionamide containing at least onecarboxylic or sulfonic acid group which will confer a negative charge tothe thionamide at a pH of 5 or below.

8. The photographic element of claim 7 wherein said layer is a silverhalide emulsion.

9. The photographic element of claim 8 wherein said thionamide ispresent in an amount of about 0.05 gram to about 30.0 grams per mole ofsilver in said silver halide emulsion.

10. The photographic element of claim 8 wherein said thionamide has thestructure wherein X is sulfur, oxygen or an iso-electronic group, R Rand R when taken separately, are aliphatic groups having up to 10 carbonatoms or substituted aliphatic groups, R and R when taken together,represent an alkylene group and R and R when taken together with thenitrogen atom to which they are attached, represent a heterocyclicgroup.

11. The photographic element of claim 8 wherein said thionamide has thestructure wherein R is an aliphatic group or a substituted aliphaticgroup containing up to 10 carbon atoms and R and R are hydrogen,aliphatic groups or substituted aliphatic groups containing up to 10carbon atoms, at least one of said groups containing a carboxylic orsulfonic acid substituent.

12. The photographic element of claim 10 wherein X in said thionamide issulfur and at least one of said groups R R and R contains a carboxylicor sulfonic acid substituent.

13. The photographic element of claim 10 wherein X in said thionamiderepresents the group NR, R being an aliphatic or substituted aliphaticgroup having up to 10 carbon atoms, and at least one of said groups R, RR and R contains a carboxylic or sulfonic acid substituent.

14. The photographic element of claim 8 wherein said thionamide ispresent in said silver halide emulsion.

15. The photographic element of claim 8 wherein said thionamide ispresent in a layer contiguous to said silver halide emulsion.

16. In a process of developing a photographic element comprising asupport coated with at least one silver halide emulsion layer, theimprovement comprising developing said photographic element in thepresence of an acyclic or monocyclic thionamide containing at least onecarboxylic or sulfonic acid group which will confer a negative chargethereto at a pH of 5 or below.

17. The process of claim 16 wherein said thionamide has the structurewherein R is an aliphatic group or a substituted aliphatic groupcontaining up to 10 carbon atoms and R and R are hydrogen, aliphaticgroups or substituted aliphatic groups containing up to 10 carbon atoms,at least one of said groups containing a car-boxylic or sulfonic acidsubstituent.

19. The process of claim 17 wherein X in said thionamide is sulfur andat least one of said groups R R and R contains a carboxylic or sulfonicacid substituent.

20. The process of claim 17 wherein X in said thionamide represents thegroup -NR, R being an aliphatic or substituted aliphatic group having upto 10 carbon atoms, and at least one of said groups R, R R and Rcontains a carboxylic or sulfonic acid substituent.

References Cited UNITED STATES PATENTS 3,433,640 3/1969 Nishio et a].96109 WILLIAM D. MARTIN, Primary Examiner R. M. SPEER, AssistantExaminer

